Method and apparatus for identifying connections between configurable nodes in a configurable integrated circuit

ABSTRACT

Some embodiments provide a method that defines a set of connections that connect the nodes in a configurable node array. The method identifies different sets of connections for connecting a set of the nodes. For each identified set of connections, the method computes a metric score that quantifies a quality of the identified set of connections. The method then selects one of the identified sets of connections to connect the configurable nodes in the array.

FIELD OF THE INVENTION

The present invention is directed towards method and apparatus foridentifying connections between configurable nodes in a configurableintegrated circuit.

BACKGROUND OF THE INVENTION

The use of configurable integrated circuits (“IC's”) has dramaticallyincreased in recent years. One example of a configurable IC is a fieldprogrammable gate array (“FPGA”). An FPGA is a field programmable ICthat has an internal array of logic circuits (also called logic blocks)that are connected together through numerous interconnect circuits (alsocalled interconnects). In an FPGA, the internal array of logic andinterconnect circuits is typically surrounded by input/output blocks.Like some other configurable IC's, the logic and interconnect circuitsof an FPGA are configurable.

FIG. 1 illustrates an array structure 100 of a prior art FPGA. As shownin this figure, the array 100 includes numerous logic circuits 105 andinterconnect circuits 110. In this architecture, the logic circuit 105are referred to configurable logic blocks (CLB's). Each CLB is formed byseveral configurable look-up tables (LUT's), where each LUT is aconfigurable logic circuit.

As shown in FIG. 1, the FPGA array structure 100 has two types ofinterconnect circuits 110 a and 110 b. Interconnect circuits 110 a areconnection boxes that connect CLB's 105 and interconnect circuit 110 bto other CLB's 105 and interconnect circuits 110 b. Interconnectcircuits 110 b, on the other hand, are switchboxes that connect theconnection boxes 110 a to other connection boxes 110 a.

Although not explicitly illustrated in FIG. 1, a CLB 105 can connect toCLB's that are several columns or several rows away from it in thearray. FIG. 2 illustrates several such connections in a priorconfigurable node architecture. Specifically, this figure illustrates anarray 205 of CLB's 210 without showing any of the intervening switch andconnection boxes. As shown in this figure, a CLB 210 a connects to CLB'sthat are one, two, three and six rows above and below it, and to CLB'sthat are one, two, three, and six columns to its right and left.

The advantage of the connection architecture illustrated in FIG. 2 isthat it allows one CLB to connect to another CLB that is much fartheraway where the distance is measured in terms of connection between twoCLB's. On the other hand, this architecture requires the use of multipleconnections to connect two CLB's that are in two different rows andcolumns. This requirement makes the connection architecture illustratedin FIG. 2 inefficient and expensive as each connection requires the useof transistor switching logic.

Also, the connection architecture illustrated in FIG. 2 is not designedto optimize the number of CLB's reachable from any given CLB.Specifically, this architecture employs the same connection scheme foreach CLB. Hence, as shown in FIG. 3, this architecture can result in acycle between two CLB's 305 and 310 in the same column, or two CLB's 315and 320 in the same row. Such cycles are undesirable as they come at theexpense of reachability of other CLB's. The uniform connectionarchitecture of FIG. 2 is also inefficient as it provides more ways thannecessary for reaching one CLB from another CLB. This redundancy isillustrated in FIG. 3, which illustrates that the CLB 325 can connect toCLB 330 through two different sets of connections, one that goes throughCLB 335 and one that goes through CLB 340. This redundancy isundesirable as it comes at the expense of reachability of other CLB's.

There is a need in the art for a configurable IC that has a wiringarchitecture that increases the interconnectivity between itsconfigurable nodes. Ideally, this wiring architecture is optimized forthe interconnectivity between the configurable nodes of the configurableIC. There is also a need for a method that identifies optimal connectionschemes for connecting the configurable nodes of a configurable IC.

SUMMARY OF THE INVENTION

Some embodiments provide a method that defines a set of connections thatconnect the nodes in a configurable node array. The method identifiesdifferent sets of connections for connecting a set of the nodes. Foreach identified set of connections, the method computes a metric scorethat quantifies a quality of the identified set of connections. Themethod then selects one of the identified sets of connections to connectthe configurable nodes in the array.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth in the appendedclaims. However, for purpose of explanation, several embodiments of theinvention are set forth in the following figures.

FIG. 1 illustrates an array structure of a prior art FPGA.

FIG. 2 illustrates several direction connections in a prior configurablenode architecture.

FIG. 3 illustrates shortcomings of the architecture presented in FIGS.2.

FIG. 4 illustrates an example of a configurable logic circuit that canperform a set of functions.

FIG. 5 illustrates an example of a configurable interconnect circuit.

FIG. 6 illustrates an example of a configurable node array.

FIGS. 7-10 illustrate several examples of configurable nodes in aconfigurable node array.

FIGS. 11 and 12 illustrate examples of two direct connections withintervening buffer circuits.

FIG. 13 presents topologic illustrations of several direct connectionsin a configurable node array of some embodiments of the invention.

FIGS. 14A-14B illustrate examples of different geometric realizationsfor some of the direct connections topologically illustrated in FIG. 11.

FIG. 15 illustrates an example of two long-offset direct connections.

FIG. 16 illustrates a configurable node array that use two differentdirect-connection schemes for two similar nodes in a configurable nodearray.

FIG. 17 illustrates a portion of a configurable node array that has fourdifferent direct-connection schemes.

FIGS. 18-21 provide topological illustrations of four direct connectionschemes that can be used as the four schemes illustrated in FIG. 17.

FIG. 22 pictorially illustrates the symmetrical relationship between thefour connection schemes illustrated in FIGS. 18-21.

FIG. 23 pictorially illustrates another possible symmetricalrelationship that can be used by four symmetrically related connectionschemes.

FIGS. 24 and 25 illustrate an optimization process that generates andexamines different direct-connection schemes for different configurablenodes in a configurable node array.

FIGS. 26-30 illustrate several examples of configurable nodes withbuilt-in turns.

FIG. 31 illustrates an example of a built-in turn in a traditionalisland style architecture.

FIG. 32 illustrates a configurable node array with a nested set ofbuilt-in turns.

FIG. 33 illustrates a configurable node array that has a set ofasymmetrical built-in turns that are repeated throughout a portion orthe entire array.

FIG. 34 illustrates a configurable IC of some embodiments of theinvention.

FIG. 35 illustrates a configuration data pool of a configurable IC ofsome embodiments of the invention.

FIG. 36 illustrates an alternative configurable IC of some embodimentsof the invention.

FIG. 37 conceptually illustrates more detailed example of a computingsystem that has a configurable IC according to some embodiments of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, numerous details are set forth for purposeof explanation. However, one of ordinary skill in the art will realizethat the invention may be practiced without the use of these specificdetails. For instance, not all embodiments of the invention need to bepracticed with the specific number of bits and/or specific devices(e.g., multiplexers) referred to below. In other instances, well-knownstructures and devices are shown in block diagram form in order not toobscure the description of the invention with unnecessary detail.

I. Definitions

A logic circuit is a circuit that can perform a function on a set ofinput data that it receives. A configurable logic circuit is a logiccircuit that can be configured to perform different functions on itsinput data set. FIG. 4 illustrates an example of a configurable logiccircuit 400 that can perform a set of functions. As shown in thisfigure, the logic circuit 400 receives a set of input data 410 and a setof configuration data 415, and provides a set of output data 420. Theconfiguration data determines the function that the logic circuitperforms on its input data. In other words, the configuration data 415causes the logic circuit to perform a particular function within its setof functions on the input data set 410. Once the logic circuit performsa function on its input data set, the logic circuit 400 provides theresult of this function as its output data set 420. The logic circuit400 is said to be configurable, as the configuration data set“configures” the logic circuit to perform a particular function. Otherexamples of configurable logic circuits can be found in United StatesPatent Application entitled “Configurable Circuits, IC's, and Systems,”filed concurrently with this application, with the Express Mail NumberEV321686171US. This Application is incorporated in the presentapplication by reference.

A configurable interconnect circuit is a circuit that can configurablyconnect an input set to an output set in a variety of manners. FIG. 5illustrates an example of a configurable interconnect circuit 500. Thisinterconnect circuit 500 connects a set of input terminals 505 to a setof output terminals 510, based on a set of configuration data 515 thatthe interconnect circuit receives. In other words, the configurationdata specify how the interconnect circuit should connect the inputterminal set 505 to the output terminal set 510. The interconnectcircuit 500 is said to be configurable, as the configuration data set“configures” the interconnect circuit to use a particular connectionscheme that connects the input terminal set to the output terminal setin a desired manner. Other examples of configurable interconnectcircuits can be found in the above-incorporated application.

A configurable node array is an array with numerous configurable nodesthat are arranged in several rows and columns. FIG. 6 illustrates anexample of a configurable node array 600 that includes 208 configurablenodes 605 that are arranged in 13 rows and 16 columns. Each configurablenode in a configurable node array is a configurable circuit thatincludes one or more configurable sub-circuits.

FIGS. 7-10 illustrate several examples of configurable nodes in anarray. Specifically, FIG. 7 illustrates a configurable node 700 that isa configurable interconnect circuit 500. Such an interconnect circuitcan be any of the interconnect circuits disclosed in theabove-incorporated application, or any switchbox, connection box,switching or routing matrix, full- or partial-cross bar, etc.Alternatively, as shown in FIG. 8, a configurable node 800 can be asimple configurable logic circuit 400. Such logic circuits can be anylook-up table (LUT), universal logic module (ULM), sub-ULM, multiplexer,PAL/PLA, etc., or any logic circuit disclosed in the above-incorporatedapplication.

FIG. 9 illustrates yet another configurable node. This node is a complexlogic circuit 900. This logic circuit is formed by multiple logiccircuits (e.g., multiple LUT's) 905 and an interconnect circuit 910. Oneexample of such a complex logic circuit is a CLB. One of ordinary skillwill realize that the illustration of the logic circuit 900 is asimplification that does not show other circuit elements (e.g.,fast-carry logic, etc.) that might be used in complex logic circuits.This illustration is provided only to convey the principle that morecomplex logic circuits are often formed by combining simpler logiccircuits and interconnect circuits. Examples of simple and complex logiccircuits can be found Architecture and CAD for Deep-Submicron FPGAs,Betz, et al., ISBN 0792384601, 1999. Other examples of logic circuitsare provided in the above-incorporated application.

FIG. 10 illustrates still another configurable node. This node 1000 isformed by a combination of a complex logic circuit (in this example, thecomplex logic circuit 900) and a complex interconnect circuit 1010(e.g., a switchbox or connection box).

In some embodiments, some or all configurable nodes in the array havethe same or similar circuit structure. For instance, in someembodiments, some or all the nodes have the exact same circuit elements(e.g., have the same set of logic gates and blocks and/or sameinterconnect circuits), where one or more of these identical elementsare configurable elements. One such example would be a set of nodes inthe array that are each formed by a particular set of LUT's andinterconnects. Having nodes with the same circuit elements simplifiesthe process for designing and fabricating the IC, as it allows the samecircuit designs and mask patterns to be repetitively used to design andfabricate the IC.

In some embodiments, the similar configurable nodes not only have thesame circuit elements but also have the same exact internal wiringbetween their circuit elements. For instance, in some embodiments, aparticular set of LUT's and interconnects that are wired in a particularmanner forms each node in a set of nodes in the array. Having such nodesfurther simplifies the design and fabrication processes as it furthersimplifies the design and mask making processes.

In some embodiments, each configurable node in a configurable node arrayis a simple or complex configurable logic circuit. In some embodiments,each configurable node in a configurable node array is a configurableinterconnect circuit. In such an array, a configurable node (i.e., aconfigurable interconnect circuit) can connect to one or more logiccircuits. In turn, such logic circuits in some embodiments might bearranged in terms of another configurable logic-circuit array that isinterspersed among the configurable interconnect-circuit array.

Several figures below illustrate several “direct connections” betweennodes in an array. A direct connection is an electrical connectionbetween two nodes that is achieved by (1) a set of wire segments thattraverse through a set of the wiring layers of the IC, and (2) a set ofvias when two or more wiring layers are involved.

In some embodiments, a direct connection might also include a set ofbuffer circuits in some cases. In other words, two nodes are directlyconnected in some embodiments by a set of wire segments that possiblytraverse through a set of buffer circuits and a set of vias. Buffercircuits are not logic or interconnect circuits. In some embodiments,buffer circuits are part of some or all direct connections. Buffercircuits might be used to achieve one or more objectives (e.g., maintainthe signal strength, reduce noise, delay signal, etc.) along the wiresegments that establish the direct connections. Inverting buffercircuits also allow an IC design to reconfigure logic circuits lessfrequently and/or use fewer types of logic circuits. In someembodiments, buffer circuits are formed by one or more inverters (e.g.,two or more inverters that are connected in series).

FIGS. 11 and 12 illustrate examples of two direct connections withintervening buffer circuits. Specifically, FIG. 11 illustrates anexample of a direct connection 1115 between two nodes 1105 and 1110. Asshown in this figure, this direct connection has an intervening buffercircuit 1120. In some embodiments, the buffer circuit 1120 is ainverter. Accordingly, in these embodiments, the direct connection 1115inverts a signal supplied by one of the nodes 1105 or 1110 to the othernode.

FIG. 12 illustrates an example of a direction connection 1215 betweentwo nodes 1205 and 1210. As shown in this figure, this direct connection1215 has two intervening buffer circuits 1220 and 1225. In someembodiments, the buffer circuits 1220 and 1225 are inverters. Hence, inthese embodiments, the direct connection 1215 does not invert a signalsupplied by one of the nodes 1205 or 1210 to the other node.

Several figures below “topologically” illustrate several directconnections between nodes in an array. A topological illustration is anillustration that is only meant to show a direct connection between twonodes without specifying a particular geometric layout for the wiresegments that establish the direct connection.

II. Direct Connections Between Offset Nodes

FIG. 13 illustrates a configurable node array 1300 of some embodimentsof the invention. This array is a part of a configurable IC that hasmultiple wiring layers. This array includes numerous configurable nodes1305 that are arranged in numerous rows and columns. In someembodiments, this array has numerous (hundreds, thousands, millions,etc.) of configurable nodes that are arranged in numerous (e.g., tens,hundreds, thousands, etc. of) rows and columns.

FIG. 13 provides a topological illustration of several directconnections between a configurable node 1305 a and several other nodesin the array 1300. As shown in this figure, the configurable node 1305 ahas direct connections with several nodes 1305 f that arehorizontally/vertically aligned with it in the array. In addition, theconfigurable node 1305 a has direct connections with nodes 1305 b, 1305c, 1305 d, and 1305 e that are not horizontally/vertically aligned withnode 1305 a. As shown in FIG. 13, nodes 1305 b, 1305 c, 1305 d, and 1305e are one row and one column away from the node 1305 a.

As mentioned above, the illustrations of the direct connections in FIG.13 are only topological illustrations. Each of these direct connectionscan be achieved by a variety of geometric realizations. In someinstances, the set of wire segments that establish a direct connectionare all on the same layer. For example, as shown in FIG. 14A, four wiresegments 1402, 1404, 1406, and 1408 can establish the direct connectionbetween nodes 1305 a and 1305 d. These four segments might be on a layer(e.g., the second wiring layer) that is different from the layer (e.g.,the first wiring layer) that has the input/output terminals 1410 and1412 of nodes 1305 a and 1305 d. Hence, in these cases, the directconnection between nodes 1305 a and 1305 d also require a set of vias1414 and 1416 to connect the wire segments 1402 and 1408 to theterminals 1410 and 1412.

In other instances, the set of wire segments that establish a directconnection between two nodes are on several wiring layers. For example,in some cases, the direct connection between nodes 1305 a and 1305 b hasa geometric realization that is similar to the representationillustrated in FIG. 13. FIG. 14B illustrates an example of thisgeometric realization. As shown in this figure, a geometric realizationcan be established by two wire segments on two different wiring layers,which are: (1) a vertical segment 1420 (on layer 2) that connects tohorizontal terminal 1422 (on layer 1) of the node 1305 a through a viaconnection 1424, and (2) a horizontal segment 1426 (on layer 3) thatconnects to vertical terminal 1428 (on layer 1) of the node 1305 bthrough a stacked via connection 1430 and connects to the verticalsegment 1420 through a via connection 1432.

When the IC uses a wiring model that allows occasional or systematicdiagonal wiring, a direct connection between two nodes can beestablished by one or more diagonal wire segments possibly inconjunction with one or more Manhattan (i.e., horizontal or vertical)segments. For the direct connection between nodes 1305 a and 1305 c,FIG. 14C illustrates an example of a geometric realization that isachieved by using a diagonal segment 1440. This diagonal segment is inthe 60°-direction on a third wiring layer, which has the 60°-directionas its preferred wiring direction. This segment connects to the verticalterminal 1442 (on layer 1) of node 1305 c and the vertical terminal 1444(on layer 1) of node 1305 a through stacked via connections 1446 and1448.

Some embodiments allow “long-offset” direct connections between twonodes in the array. A “long-offset” connection is a direct connectionbetween two nodes in the array that are offset by more than one row andat least one column, or more than one column and at least one row. Asmentioned above, a direct connection might include one or more buffercircuits that are connected to the wire segments of the directconnection. In some embodiments, such buffer circuits are more likely tobe used for longer connections than for the shorter connections, assignal strength is a more pressing issue for longer connections.

FIG. 15 illustrates an example of two long-offset direct connections.This figure illustrates a configurable node array 1500 that has aconfigurable node 1505. This configurable node 1505 has two long-offsetdirect connections 1510 and 1515, which are topologically illustrated inFIG. 15. The first direct connection 1510 connects node 1505 to node1520, which is above node 1505 by three rows and is to the left of thenode 1505 by one column. The second direct connection 1515 connects node1505 to node 1525, which is below node 1505 by two rows and is to theright of the node 1505 by two columns.

Table 1 below identifies the direct connections of node 1505. This tableidentifies a direct connection between node 1505 and one of itsneighboring nodes in terms of two coordinates. These two coordinates area delta-column coordinate and a delta-row coordinate, which specify thecolumn and row offset between the particular node and the connectedneighboring node. TABLE 1 Direct Connections of Node 1505 Delta-ColumnDelta-Row 2 0 3 0 1 1 0 1 0 2 −1 1 −1 3 −1 0 −2 0 −1 −1 2 −2III. Different Direct-Connections Schemes

Some embodiments of the invention use several different directconnection schemes for same types of nodes in a configurable node array.FIG. 16 illustrates one such embodiment. Specifically, this figureillustrates a configurable node array 1600 that use two differentdirect-connection schemes for two node 1605 and 1610 in the array.

The nodes 1605 and 1610 are of the same type. In some embodiments, twonodes are of the same type when they have the same circuit elements withone or more of these identical elements being configurable. In someembodiments, two nodes of the same type also have the same internalwiring between their identical circuit elements. For instance, in someembodiments, the nodes 1605 and 1610 are two switchboxes that have thesame component circuit elements and interconnect wiring between thecircuit elements.

Tables 2 and 3 below respectively identify the direct connections ofnodes 1605 and 1610. Like Table 1, each of these tables identifies adirect connection between a particular node and one of its neighboringnodes in terms of two coordinates, a delta-column coordinate and adelta-row coordinate. For instance, the third record in Table 2specifies a delta-column coordinate of −1 and a delta-row coordinate of0. This record specifies a direct connection between node 1605 and thenode 1615 directly to the left of it. Alternatively, the fifth record inTable 3 specifies a delta-column coordinate of 2 and a delta-rowcoordinate of 2. This record specifies a direct connection between node1610 and the node 1620, which is two rows above and two columns to theright of node 1610. TABLE 2 Direct Connections of Node 1605 Delta-ColumnDelta-Row 1 0 0 1 −1 0 0 −1 2 0 3 3 −3 2 −1 1 −1 −2 1 −3 1 −1

TABLE 3 Direct Connections of Node 1610 Delta-Column Delta-Row 1 0 0 1−1 0 0 −1 2 2 1 1 −1 1 −2 −1 −1 −1 1 −2 1 −1

Some embodiments of the invention use several different directconnection schemes for similar node types in a configurable node array.One such embodiment is illustrated in FIG. 17. This figure illustrates aportion of a configurable node array 1700 that has four differentdirect-connection schemes. Specifically, each node in this array has oneof four direct connection schemes, as illustrated by the labels 1, 2, 3,and 4 in FIG. 17.

FIGS. 18-21 provide topological illustrations of four direct connectionschemes that can be used as the four schemes illustrated in FIG. 17.Table 4 below identifies the four direct connection schemes illustratedin FIGS. 18-21. This table identifies each connection scheme in terms ofeight vectors, where each vector is specified as a pair of delta-columnand delta-row coordinates. For instance, the eighth column, third row ofTable 4 identifies the seventh direct-connection vector of the secondconnection scheme as a vector with the coordinates −1,2. This vectorspecifies a direct connection between a node 1905 and a node 1910 thatis one column to the left of and two rows above the node 1905. TABLE 4Direct Connection Schemes 1800-2100 Connection 1^(st) 2^(nd) 3^(rd)4^(th) 5^(th) 6^(th) 7^(th) 8^(th) Scheme Vector Vector Vector VectorVector Vector Vector Vector 1 (1800) 1, 0 0, 1 −1, 0     0, −1 1, 1 −3,0 2, 1 8, 8 2 (1900) 0, 1 −1, 0     0, −1 1, 0 −1, 1     0, −3  −1, 2  −8, 8   3 (2000) −1, 0     0, −1 1, 0 0, 1   1, −1 −3, 0   2, −1   8, −84 (2100)   0, −1 1, 0 0, 1 −1, 0   −1, −1   0, 3 −1, −2 −8, −8

As indicated in Table 4, each of the four connection schemes illustratedin FIGS. 18-21 has direct connections with its four closest horizontallyand vertically aligned neighbors. Each of these connection schemes alsohas four long-offset direct connections. These connections areidentified as the fifth, sixth, seventh, and eighth vectors in Table 4.

As apparent from the numerical values of the vectors specified in Table4, the connection schemes illustrated in FIGS. 18-21 have a symmetricalrelationship with respect to each other. According to this symmetricalrelationship, each vector (a, b) in the first connection scheme(illustrated in FIG. 18) has a corresponding symmetrically relatedvector in each of the other three connection schemes. Thesesymmetrically related vectors in the second, third, and fourthconnection schemes respectively are: (−b,a), (a,−b), and (−b,−a). Forexample, the seventh vector (2, 1) in the first connection scheme issymmetrically related to the following vectors in the second, third, andfourth connection schemes: (−1, 2), (2, −1), and (−1, −2).

FIG. 22 pictorially illustrates the symmetrically related seventhvectors in these four connection schemes. FIG. 22 also illustratesanother way of expressing the symmetrical relationship between vectorsin the four connection schemes of FIGS. 18-21. As shown in FIG. 22, (1)each vector (e.g., the 5^(th) vector) in the second connection scheme1900 is 90° rotated in the counterclockwise direction with respect toits corresponding vector (e.g., the 5^(th) vector) in the firstconnection scheme 1800, (2) each vector in the third connection scheme2000 is 45° rotated in the clockwise direction with respect to itscorresponding vector in the first connection scheme 1800, and (3) eachvector in the fourth connection scheme 2100 is 135° rotated in theclockwise direction with respect to its corresponding vector in thefirst connection scheme 1800.

Other embodiments use other symmetrical relationships to generate othersets of symmetrical connection schemes. FIG. 23 illustrates analternative symmetrical relationship between four connection schemes.According to this symmetrical relationship, each vector in a firstconnection scheme has a corresponding symmetrically related vector ineach of three other connection schemes. Specifically, a vector 2305 inthe first connection scheme has (1) a corresponding vector 2310 in thesecond connection scheme, which is identical to vector 2305 except thatit has been rotated by an angle A in the clockwise direction, (2) acorresponding vector 2315 in the third connection scheme, which isidentical to vector 2305 except that it has been rotated by an angle B(where B equals (360−A)/3) in the counterclockwise direction, and (3) acorresponding vector 2320 in the fourth connection scheme, which isidentical to vector 2305 except that it has been rotated by an angle 2*Bin the counterclockwise direction.

One of ordinary skill will realize that other embodiment might use feweror more connection schemes for nodes of the same type in a configurablenode array. For instance, some embodiments might only use two connectionschemes. Also, in other embodiments, some or all of the connectionschemes are not symmetrically related to the other connections schemes.In addition, some embodiments do not include unit vectors or the sameset of unit vectors in each connection scheme. Furthermore, in someembodiments, the different connection schemes define different number oflong-offset direct connections for the same type of configurable nodes.

IV. Process for Specifying Different Direct-Connection Schemes

Some embodiments of the invention provide a method that defines a set ofconnections for connecting nodes in a configurable node array, which, insome embodiments, are the same type of nodes. This method examinesseveral different sets of connections for connecting a set of the nodes.In each of the identified sets, the method then computes a metric scorethat quantifies a quality of the identified set of connections inconnecting the configurable nodes. The method then selects at least oneof the identified sets of connections for connecting the configurablenodes in the array.

Different embodiments might use different metric scores that optimizedifferent qualities of the connection sets. For instance, in someembodiments, the metric score might express the number of nodesreachable from a node. This metric score optimizes the overallreachability. In other embodiments, the metric score might expresslength constraints, reconvergence, reachability within a particularnumber of “hops,” prioritized reachability, etc. (where a hop is adirect connection between two nodes).

Different embodiments use different optimization techniques to optimizethe metric score that quantifies the quality of the identified set ofconnections. For instance, some embodiments use complex constrainedoptimization techniques, such as local optimization, simulatedannealing, etc. Other embodiments use less complex techniques. Oneexample of a simple constrained optimization technique is illustrated inFIG. 24. Specifically, this figure illustrates a process 2400 thatrandomly generates and examines different direct-connection schemes fordifferent configurable nodes in a configurable node array. This processtries to identify a set of connection schemes that enables a maximallydispersed exploration of a node graph that corresponds to a configurablenode array.

As shown in this figure, the process 2400 initially generates (at 2405)a candidate connection-vector set for a single direct-connection scheme.In some embodiments, the candidate-vector set generated at 2405 includesonly the direct-connection vectors that will differ among thedirect-connection schemes specified by the process 2400. For instance,the process does not generate any unit vectors at 2405 when eachdirect-connection scheme is to have the same set of unit vectors. Insome embodiments, the process generates (at 2405) the candidateconnection-vector set randomly based on a set of constraints, such asthe number of vectors in the set, the maximum length for any givenvector, etc.

After 2405, the process determines (at 2410) whether the candidate setgenerated at 2405 is an acceptable candidate set. In some embodiments,the process makes this determination by checking whether the specifiedset meets a set of constraints. These constraints can relate to somedesired numerical attribute or attributes of the candidate vector set(such as the average length of vectors in the set, the maximum edgelength, the total edge length) or some other constraint related to thecandidate vector set (e.g., congestion based metrics based on theexpected congestion caused by a candidate vector set). Some embodimentsuse only one constraint (e.g., the average vector length) while otherembodiments use multiple constraints. Also, some embodiments computevector lengths by assuming a Euclidean (“all-angle”) wiring, while otherembodiments compute lengths based on other wiring models, such as aManhattan model, an octilinear model, a hexalinear model, etc.

When the process determines (at 2410) that the candidate vectors set isacceptable, the process evaluates (at 2420) the candidate vector set.One example of such an evaluation will be described below by referenceto FIG. 25. As further described below, the evaluation process of FIG.25 generates other candidate vector sets that have a symmetricalrelationship to the vector set specified at 2405, and then uses all thecandidate sets to compute a metric score that relates to the number ofunique nodes that are reachable from other nodes through differentnumber of hops, where, as mentioned above, a hop refers to a directconnection between two nodes.

After evaluating the candidate vector set, the process determines (at2425) whether the candidate vector set resulted in the best solutionthat it has generated thus far. In some embodiments, the process makesthe determination at 2425 based on the metric score computed by theevaluation process at 2420. If the process determines (at 2425) that thecandidate vector set did not result in the best solution, the processtransitions to 2415, which will be further described below. On the otherhand, when the candidate vector set results in the best solution, theprocess records (at 2430) the candidate vector set as the best solution.In some embodiments, the process records (at 2430) not only thecandidate vector set specified at 2405 but also its symmetricallyrelated vector sets that the evaluation process 2500 of FIG. 25generates. After 2430, the process transitions to 2415. The process alsotransitions to 2415 when it determines (at 2410) that the candidatevector set is not acceptable.

At 2415, the process determines whether it has examined sufficientnumber of candidate vector sets. When the process determines (at 2415)that it has examined a sufficient number of candidate vector sets, theprocess returns to 2405 to start its operation again. Otherwise, theprocess ends. In some embodiments, the process 2400 loops automaticallywithout the stopping criteria at 2415, until the process is stopped byan operator or another process.

FIG. 25 illustrates a process 2500 that some embodiments use to performthe evaluation operation 2420 of the process 2400. As shown in thisfigure, the process 2500 initially generates (at 2505) other candidatevector sets that have a symmetrical relationship to the vector setspecified at 2405. In some embodiments, the process 2500 generates thevector sets by using one of the symmetrical relationships that weredescribed above by reference to FIGS. 18-23.

Next, in some embodiments, the process adds (at 2510) to each vector setthe set of vectors that are common among the vectors sets. For instance,in some embodiments, each vector set will include the four unit vectorsin the horizontal and vertical directions (i.e, will include (1,0),(0,1), (−1,0), and (0,−1)). Accordingly, in these embodiments, theprocess adds (at 2510) these four unit vectors to each vector set.

After 2510, the process selects (at 2515) a node in the array as itsorigin. In some embodiments, this node is the node that is closest tothe center of the array. Based on the candidate vector sets generated at2505 and completed at 2510, the process then calculates (at 2520) allnodes that can be reached from the designated node origin in differentnumber of hops (e.g., 1, 2, 3, etc.). Some embodiments use abreadth-first search to perform this calculation.

Based on the calculated numbers, the process then computes a metricscore at 2525. Some embodiments use the following equation to compute ametric score. $\begin{matrix}{{{Score} = \frac{{\sum\limits_{i = 0}^{X}\quad{i*{R(i)}}} - {R\left( {i - 1} \right)}}{R(X)}},} & (1)\end{matrix}$where R is the calculated number of nodes that are reachable within oneto i hops, n is the number of rows or number of columns, in a node arraythat may or may not be a square array, and X is an integer (e.g., 5, 10,100, 1000, etc.). This score approximates the expected length from theorigin (i.e., the node selected at 2515) to a random node in the array.

Other embodiments use either of the following equations in place of, orin conjunction with, the equation (1) above. $\begin{matrix}{{{Score} = {\sum\limits_{i = 0}^{10}\quad\frac{R(i)}{i}}},} & {(2),} \\{{{Score} = {\sum\limits_{i = 0}^{10}\quad\frac{R(i)}{i^{2}}}},} & {(3),}\end{matrix}$where R and i are as defined above for equation (1). To use the scoresof several of the above equations in conjunction with each other, someembodiments compute a blended sum of these scores.

After 2525, the process 2500 ends.

Table 5 provides metric scores that are generated by equation (1) fordifferent connection schemes that are produced by using the processes2400 and 2500 of FIGS. 24 and 25 under different sets of constraints fordifferent sized node arrays. The constraints are the number ofnon-unit/offset vectors in the connection scheme and the total length ofthe non-unit/offset vectors. Each of these connections schemes also hasfour unit vectors connecting the node to its four nearest neighboringnodes in the horizontal and vertical directions. Table 5 alsoillustrates the number of nodes that are reachable from a given node inthree hops on average. TABLE 5 Total Length Number of Offset of Offsetor Score in a Score in a Score in a Nodes or Non-Unit Non-Unit 100 × 10070 × 70 node 40 × 40 node reachable Vectors Vectors node array arrayarray in 3 hops 4 80 7.95 6.64 4.89 115.5 4 128 6.81 5.65 4.26 340 4 1766.06 5.17 3.92 477.5

Table 6 provides a comparable set of numbers for a configurable nodearray that is interconnected through the prior art connection schemeillustrated in FIG. 2. Specifically, the second row in this tableidentifies the equation (1) metric score and hop data for a connectionscheme that connects each node to nodes that are one, two, or threeunits away from it in the horizontal or vertical directions. The thirdrow identifies the score and hop data for a connection scheme thatconnects each node to nodes that are one, two, six units away from it inthe horizontal or vertical directions. The fourth row identifies thescore and hop data for a connection scheme that connects each node tonodes that are one, two, three, or six units away from it in thehorizontal or vertical directions. TABLE 6 Total Length of Offset/ Scorein a Score in a Score in a Nodes Non-Unit 100 × 100 70 × 70 node 40 × 40node reachable Vectors Vectors node array array array in 3 hops (0,1)(1, 0)(0, −1)(−1, 0) 80 17.3 12.3 7.35 145 (0, 2)(2, 0)(0, −2)(−2, 0)(0, 3)(3, 0)(0, −3)(−3, 0) (0, 1)(1, 0)(0, −1)(−1, 0) 128 10.1 7.7 5.12241 (0, 2)(2, 0)(0, −2)(−2, 0) (0, 6)(6, 0)(0, −6)(−6, 0) (0, 1)(1,0)(0, −1)(−1, 0) 176 9.82 7.33 4.8 321 (0, 2)(2, 0)(0, −2)(−2, 0) (0,3)(3, 0)(0, −3)(−3, 0) (0, 6)(6, 0)(0, −6)(−6, 0)

The second, third, and fourth rows in Table 6 are comparable to thesecond, third, and fourth rows in Table 5 as the total length of vectorsof the connection schemes of these rows are equal. As it can be seen bycomparing the score and hop data of the comparable rows in Tables 5 and6, the connection schemes that result from the constraints specified inTable 5 result in distinctly better scores and hop values. Such betterscores and hop values are because the processes 2400 and 2500 examinenumerous connection schemes and select the one that results in the bestmetric score.

Although the processes 2400 and 2500 was described above, one ofordinary skill will realize that other embodiments can use a variety ofother processes to specify different direct-connection schemes fordifferent configurable nodes in a configurable node array. As mentionedabove, these processes might use a variety of other optimizationtechniques, such as local optimization, simulated annealing, etc. Also,some embodiments use several different connection schemes for aconfigurable node array, with at least two of the connection schemesspecifying a different number of long-offset direction connections(e.g., one connection scheme might specify four long-offset directconnections, while another connection scheme might specify sixlong-offset direct connections).

Instead of generating a first connection scheme and generating the otherconnection schemes based on the first scheme, some embodiments mightpartially generate two or more of the connection schemes and thengenerate the remaining connections based on symmetrical relationshipswith the partially generated connections of the two or more connectionschemes. For instance, some embodiments might generate one vector foreach connection scheme, and then rotate each of these vectors throughthe various symmetrical angles in order to generate the additionalvectors of the connection schemes. Alternatively, some embodiments mightcompletely generate two or more of the connection schemes independentlyfrom each other.

As mentioned above, the process 2500 selects (at 2515) one node in thearray and computes (at 2520) the number of nodes reachable from theselected node in a set number of hops. This process then uses thecomputed number of nodes in calculating its metric score at 2525. Otherembodiments, however, select (at 2515) several different nodes in thearray, calculate (at 2520) the number of nodes reachable from theseselected nodes, and then compute (at 2525) the metric score based on thenumber calculated at 2520. For instance, some embodiments calculate (at2520) the number of reachable nodes for each node in the array. Some ofthese embodiments then (at 2520) generate an average of these numbers,and use (at 2525) this generated average to generate their metric scoresat 2525.

V. Configurable Node Array with Built-in Turns

Some embodiments of the invention are IC's with configurable node arraysthat have a systematic series of build-in turns. Such turns can bearranged in a variety of different architectural schemes, such assymmetrical schemes, asymmetrical schemes, nested schemes, anycombination of symmetrical, asymmetrical, and/or nested schemes, etc.

FIGS. 26-30 illustrate several examples of symmetrical schemes. FIG. 26illustrates a configurable node array 2600 that has numerousconfigurable nodes 2605, which are arranged in numerous rows andcolumns. In some embodiments, the configurable nodes 2605 are all thesame type of nodes. For instance, in some embodiments, all the nodeshave the same circuit structure (e.g., the same circuit elements). Insome embodiments, similar type nodes have the same circuit elements andthe same internal wiring between the circuit elements.

In some embodiments, the array 2600 has numerous direct connections (notshown) between pairs of neighboring nodes that are horizontally orvertically aligned (i.e., that are in the same row or column in thearray). FIG. 27 illustrates one such set of direct connections 2710 fora node 2705 in the array 2600. Some embodiments have such directconnections between each pair of horizontally or vertically alignednodes in the array. In conjunction or instead of such connectionsbetween pairs of neighboring aligned nodes, the configurable node array2600 in some embodiments also has direct connections betweenhorizontally or vertically aligned nodes that are not neighboring nodesin the array. For instance, FIG. 27 illustrates that the array 2600 has,in some embodiments, a node 2715 that connects to non-neighboring nodes2720, 2725, and 2730 that are horizontally aligned with node 2715. Thisfigure also illustrates that the node 2720 connects to non-neighboringnodes 2735, 2740, and 2745 that are vertically aligned with it.

In addition to the direct connections between horizontally andvertically aligned nodes, the array 2600 includes numerous directconnections 2610 between nodes that are offset in the array.Specifically, as shown in FIG. 26, the array includes numerous directionconnections 2610, where each such connection couples two nodes that aretwo columns and three rows separated in the array.

Such connections 2610 are referred to as “built-in turns.” Built-inturns allow two offset nodes to be connected by relying on wiringarchitecture that reduces the number of interconnect circuits necessaryfor establishing the connection between the two nodes. For instance, asshown in FIG. 26, a built-in turn 2610 a couples two offset nodes 2605 aand 2605 b without using any intervening interconnect circuit.

In some cases, built-in turns do not eliminate the need to rely onintervening interconnect circuits, but instead reduce the number ofintervening interconnect circuits. For instance, in FIG. 27, nodes 2715and 2750 can be connected through (1) the horizontal connection 2755that connects nodes 2715 and 2720, (2) node 2720's interconnect circuit(not shown) that allows a change of direction in the set of connectinghops, (3) the vertical connection 2760 that connects nodes 2720 and2740, (4) node 2740's interconnect circuit (not shown) that relays thesignal on its input terminal connected to connection 2760 to its outputterminal connected to connection 2765, and (5) the vertical connection2765 between neighboring nodes 2740 and 2750.

Alternatively, as shown in FIG. 27, nodes 2715 and 2750 can be connectedthrough (1) the built-in turn connection 2770 that connects nodes 2715and 2740, (2) node 2740's interconnect circuit that relays the signal onits input terminal connected to connection 2770 to its output terminalconnected to connection 2765, and (3) the vertical connection 2765between neighboring nodes 2740 and 2750. Accordingly, this alternativeconnection scheme connects the two nodes 2715 and 2750 in two hopsinstead of the three hops that are required to connect these two nodesthrough nodes 2720 and 2740. Such a reduction typically reduces thelength, and associated delay, of the wire segments necessary toestablish the connection between two offset nodes.

Also, the alternative connection scheme that uses the turn connection2770 reduces reliance on intervening interconnect circuits byeliminating node 2720's interconnect circuit from the connection path.Reducing the number of intervening interconnect circuits is oftendesirable. The use of interconnect circuits adversely affects the IC'soperational speed, because it requires signals (1) to traverse from thehigher wiring layers to the IC's substrate for processing by therelatively slow transistor-level logic and then (2) to traverse back tothe higher wiring layers from the IC's substrate. Interconnect circuitsalso take valuable real estate on an IC. Therefore, it is oftendesirable to minimize the use of interconnect circuits so that they canbe used only in situations were they are required.

Each built-in turn 2610 in FIGS. 26 and 27 is established by (1) a setof wire segments that traverse through a set of the IC's wiring layers,(2) a set of vias when two or more wiring layers are involved, and (3)possibly a set of buffer circuits. In some embodiments, all the wiresegments of all built-in turns 2610 are on the same wiring layer (e.g.,layer 4). In these embodiments, no built-in turn 2610 requires a via toconnect the turn's four wire segments to each other. (The turns,however, might still require vias to connect to the input and outputterminals of nodes in the array.)

Alternatively, different wire segments of the built-in turns 2610 mightbe on different wiring layers. For instance, FIGS. 28 and 29 illustratean alternative architecture for the array 2600 where all the horizontalsegments 2800 and 2805 of the turns 2610 are on one wiring layer (e.g.,the fourth layer), while all the vertical segments 2810 and 2815 of theturns 2610 are on another wiring layer (e.g., the fifth layer). Such anarrangement would require each turn 2610 to have several (e.g., three)vias to connect its four wire segments 2800, 2805, 2810, and 2815 toeach other.

Yet other alternative arrangements can be used in other embodiments,where the wire segments of different built-in turns 2610 of the array2600 are arranged differently. For instance, in some embodiments,different turns 2610 might have their wiring segments on differentwiring layers (e.g., some might have their horizontal segments on layer4, while others might have their horizontal segments on layer 5). Also,in some embodiments, some turns 2610 might have all their segments onthe same wiring layer, while other turns 2610 might have their wiringsegments on different wiring layers.

As illustrated in FIGS. 26 and 27, the built-in turns 2610 are a set ofturns that are systematically arranged across the entire node array or aportion of this array. These turns are arranged symmetrically in someembodiments. For instance, as illustrated FIG. 26, the turns 2610 can becategorized into four sets of turns that are horizontally and/orvertically symmetrically laid out in the array 2600 about an origin 2680in the array. These four sets are in four quadrants 2650, 2655, 2660,and 2665 of a coordinate system that is specified by an x- and y-axes2670 and 2675 running through the origin 2680. Each particular set has asymmetrical relationship with the other three sets, as flipping theparticular set about the origin in the horizontal and/or verticaldirections can generate the other three sets.

Some embodiments define multiple sets of built-in turns that havemultiple sets of symmetrical relationships with each other. Forinstance, in addition to the four sets of symmetrically arranged turns2610 of FIG. 26, some embodiments define another set of turns that aresymmetrical to each other and perhaps to the turns 2610. For the array2600, FIG. 30 illustrates another set of symmetrically arranged turns3010. Each of the turns 3010 connects two nodes 2605 in the array thatare separated by three columns and two rows.

Like each turn 2610, each turn 3010 can be established by (1) a set ofwire segments that traverse through a set of the IC's wiring layers, (2)a set of vias when two or more wiring layers are involved, and (3)possibly one or more buffer circuits. Like the turns 2610, the turns3010 can also be categorized into four sub-sets of turns that are laidout horizontally and/or vertically symmetrically in the array an origin3015 in the array. In addition, the turns 3010 are symmetrically relatedto the turns 2610 as they are rotated versions of the turns 2610.

As mentioned above, the configurable nodes 2605 are all the same type ofnodes in some embodiments. For instance, in some embodiments, all thenodes have the same circuit structure (i.e., the same circuit elements)and perhaps the same internal wiring. One example of such nodes would beswitch boxes in a traditional island style architecture. FIG. 31illustrates an example of a built-in turn 2610 in this architecture.

Although several sets of built-in turns were described above byreference to FIGS. 26-31, one of ordinary skill will realize that otherembodiments might use numerous other styles of built-in turns, as wellas numerous other architectural layouts of such turns. For instance, theconfigurable node array 2600 does not have the direct connectionsbetween nodes 2715, 2720, 2725, and 2730, and/or between nodes 2720,2735, 2740, and 2745 in some embodiments.

Also, FIG. 32 illustrates a configurable node array 3200 with a nestedset of built-in turns. This set of turns includes five turns 3205, 3210,3215, 3220, and 3225 that connect five pairs of nodes. FIG. 33illustrates a configurable node array 3300 that has a set ofasymmetrical built-in turns that are repeated throughout a portion orthe entire array. This asymmetrical set includes three turns 3305, 3310,and 3315.

Like the turns illustrated in FIGS. 26-30, the turns illustrated inFIGS. 32 and 33 can defined by (1) a set of wire segments that traversethrough a set of the IC's wiring layers, (2) a set of vias when two ormore wiring layers are involved, and (3) possibly a set of buffercircuits. For instance, in some embodiments, the turns in FIGS. 32 and33 are on the same wiring layer (e.g., layer 4). In these embodiments,no built-in turn requires a via to connect the turn's wire segments toeach other. (The turns, however, might still require vias to connect tothe input and output terminals of nodes in the array.) Alternatively, insome embodiments, different wire segments of the built-in turns are ondifferent wiring layers. Also, as mentioned above, some embodiments usea combination of symmetrical, asymmetrical, and/or nested turns.

VI. Configurable IC and System

FIG. 34 illustrates a portion of a configurable IC 3400 of someembodiments of the invention. As shown in this figure, this IC has aconfigurable node array 3405 and I/O circuitry 3410. The node array 3405can be any of the invention's configurable nodes arrays that weredescribed above. The I/O circuitry 3410 is responsible for routing databetween the configurable nodes 3415 of the array 3405 and circuitsoutside of the array (i.e., circuits outside of the IC, or within the ICbut outside of the array 3405). As further described below, such dataincludes data that needs to be processed or passed along by theconfigurable nodes.

The data also includes in some embodiments configuration data thatconfigure the nodes to perform particular operations. FIG. 35illustrates a more detailed example of this. Specifically, this figureillustrates a configuration data pool 3505 for the configurable IC 3400.This pool includes N configuration data sets (CDS). As shown in FIG. 35,the input/output circuitry 3410 of the configurable IC 3400 routesdifferent configuration data sets to different configurable nodes of theIC 2600. For instance, FIG. 35 illustrates configurable node 3545receiving configuration data sets 1, 3, and J through the I/O circuitry,while configurable node 3550 receives configuration data sets 3, K, andN-1 through the I/O circuitry. In some embodiments, the configurationdata sets are stored within each configurable node. Also, in someembodiments, a configurable node can store multiple configuration datasets so that it can reconfigure quickly by changing to anotherconfiguration data set. In some embodiments, some configurable nodesstore only one configuration data set, while other configurable nodesstore multiple such data sets.

A configurable IC of the invention can also include circuits other thanthe configurable node array and I/O circuitry. For instance, FIG. 36illustrates one such IC 3600. This IC has a configurable block 3650,which includes a configurable node array 3405 and I/O circuitry 3410 forthis array. It also includes a processor 3615 outside of the array, amemory 3620, and a bus 3610, which conceptually represents allconductive paths between the processor 3615, memory 3620, and theconfigurable block 3650. As shown in FIG. 36, the IC 3600 couples to abus 3630, which communicatively couples the IC to other circuits, suchas an off-chip memory 3625. Bus 3630 conceptually represents allconductive paths between the components of the IC 3600.

This processor 3615 can read and write instructions and/or data from anon-chip memory 3620 or an offchip memory 3625. The processor 3615 canalso communicate with the configurable block 3650 through memory 3620and/or 3625 through buses 3610 and/or 3630. Similarly, the configurableblock can retrieve data from and supply data to memories 3620 and 3625through buses 3610 and 3630.

FIG. 37 conceptually illustrates a more detailed example of a computingsystem 3700 that has an IC 3705, which includes one of the invention'sconfigurable node arrays that were described above. The system 3700 canbe a stand-alone computing or communication device, or it can be part ofanother electronic device. As shown in FIG. 37, the system 3700 not onlyincludes the IC 3705, but also includes a bus 3710, a system memory3715, a read-only memory 3720, a storage device 3725, input devices3730, output devices 3735, and communication interface 3740.

The bus 3710 collectively represents all system, peripheral, and chipsetinterconnects (including bus and non-bus interconnect structures) thatcommunicatively connect the numerous internal devices of the system3700. For instance, the bus 3710 communicatively connects the IC 3710with the read-only memory 3720, the system memory 3715, and thepermanent storage device 3725.

From these various memory units, the IC 3705 receives data forprocessing and configuration data for configuring the IC's configurablelogic and/or interconnect circuits. When the IC 3705 has a processor,the IC also retrieves from the various memory units instructions toexecute. The read-only-memory (ROM) 3720 stores static data andinstructions that are needed by the IC 3710 and other modules of thesystem 3700. The storage device 3725, on the other hand, isread-and-write memory device. This device is a non-volatile memory unitthat stores instruction and/or data even when the system 3700 is off.Like the storage device 3725, the system memory 3715 is a read-and-writememory device. However, unlike storage device 3725, the system memory isa volatile read-and-write memory, such as a random access memory. Thesystem memory stores some of the instructions and/or data that the ICneeds at runtime.

The bus 3710 also connects to the input and output devices 3730 and3735. The input devices enable the user to enter information into thesystem 3700. The input devices 3730 can include touch-sensitive screens,keys, buttons, keyboards, cursor-controllers, microphone, etc. Theoutput devices 3735 display the output of the system 3700.

Finally, as shown in FIG. 37, bus 3710 also couples system 3700 to otherdevices through a communication interface 3740. Examples of thecommunication interface include network adapters that connect to anetwork of computers, or wired or wireless transceivers forcommunicating with other devices. One of ordinary skill in the art wouldappreciate that any other system configuration may also be used inconjunction with the invention, and these system configurations mighthave fewer or additional components.

While the invention has been described with reference to numerousspecific details, one of ordinary skill in the art will recognize thatthe invention can be embodied in other specific forms without departingfrom the spirit of the invention. Thus, one of ordinary skill in the artwould understand that the invention is not to be limited by theforegoing illustrative details, but rather is to be defined by theappended claims.

1-20. (canceled)
 21. A method of designing an integrated circuit (IC)comprising a plurality of configurable nodes, the method comprising: a)identifying a plurality of different direct connection schemes forconnections between configurable nodes; b) computing a cost for each ofsaid plurality of different direct connection schemes; and c) selectinga first direct connection scheme for a first set of configurable nodesbased on the computed costs.
 22. The method of claim 21 furthercomprising selecting a second direct connection scheme for a second setof configurable nodes based on the computed costs.
 23. The method ofclaim 22, wherein a computed cost for the IC is lower when both thefirst and second direct connection schemes are selected than when eitheris selected without the other.
 24. The method of claim 21 furthercomprising selecting a plurality of direct connection schemes for aplurality of sets of configurable nodes based on the computed costs. 25.The method of claim 24, wherein a computed cost for the IC is lower whenall of said selected plurality of direct connection schemes are selectedthan when any subset is selected without the others.
 26. A method ofdesigning an integrated circuit (IC) comprising a plurality ofconfigurable nodes, the method comprising: a) generating a first directconnection scheme comprising a set of direct connections from aparticular configurable node to a first set of configurable nodes towhich said particular configurable node is directly connected in saidfirst direct connection scheme; b) computing a score for said firstdirect connection scheme based on applying said first direct connectionscheme to each of at least two configurable nodes of said plurality ofconfigurable nodes; c) generating a second direct connection schemecomprising a set of direct connections from said particular configurablenode to a second set of configurable nodes to which said particularconfigurable node is directly connected in said second direct connectionscheme; d) computing a score for said second direct connection schemebased on applying said second direct connection scheme to each of atleast two configurable nodes of said plurality of configurable nodes;and e) selecting a direct connection scheme for implementing on said ICbased on a score of said direct connection scheme.
 27. The method ofclaim 26 further comprising: a) generating a plurality of directconnection schemes, each direct connection scheme of said plurality ofdirect connection schemes comprising a set of direct connections fromsaid particular configurable node to a particular set of configurablenodes to which said particular configurable node is directly connectedin said direct connection scheme; and b) computing a score for eachdirect connection scheme of said plurality of direct connection schemes,wherein said score is based on applying said direct connection scheme toeach of at least two configurable nodes of said plurality ofconfigurable nodes.
 28. The method of claim 26, wherein computing ascore for a direct connection scheme comprises determining anexpectation value of a length of a connection from said particularconfigurable node to a random configurable node of said IC.
 29. Themethod of claim 26, wherein said first and second sets are generatedbefore either of said scores are computed.
 30. The method of claim 26,wherein said score for said first direct connection scheme is computedbefore said second direct connection scheme is generated.
 31. The methodof claim 26, wherein computing a score for a direct connection schemecomprises determining a number of configurable nodes reachable from agiven configurable node when said direct connection scheme is applied tosaid plurality of configurable nodes.
 32. The method of claim 26,wherein generating said first direct connection scheme comprisesselecting a random set of direct connections.
 33. The method of claim32, wherein generating said first direct connection scheme furthercomprises adding a set of unit length direct connections to said randomset of direct connections.
 34. The method of claim 32, whereingenerating said first direct connection scheme further comprises addinga set of direct connections that are symmetrical to said random set ofdirect connections.
 35. The method of claim 34, wherein said set ofdirect connections that are symmetrical to said random set of directconnections comprises a set of direct connections in which: a) eachdirect connection corresponds to a direct connection of said random setof direct connections, and b) each direct connection is rotated by asame angle relative to the corresponding direct connection of saidrandom set of direct connections.
 36. The method of claim 34, whereinsaid set of direct connections that are symmetrical to said random setof direct connections comprises a set of direct connections in which: a)each direct connection corresponds to a direct connection of said randomset of direct connections, and b) each direct connection is reflectedabout an axis relative to the corresponding direct connection of saidrandom set of direct connections.
 37. A method of designing anintegrated circuit (IC) comprising multiple pluralities of configurablenodes, the method comprising: a) generating a first set of directconnection schemes, each direct connection scheme comprising a set ofdirect connections from a particular configurable node to a set ofconfigurable nodes to which said particular configurable node isdirectly connected in said direct connection scheme; b) generating asecond set of direct connection schemes, each direct connection schemecomprising a set of direct connections from a particular configurablenode to a set of configurable nodes to which said particularconfigurable node is directly connected in said direct connectionscheme; c) computing a score for said first set of direct connectionschemes based on applying each direct connection scheme of said firstset of direct connection schemes to at least one set of configurablenodes of said plurality of sets of configurable nodes; d) computing ascore for said second set of direct connection schemes based on applyingeach direct connection scheme of said second set of direct connectionschemes to at least one set of configurable nodes of said plurality ofsets of configurable nodes; and e) selecting a set of direct connectionschemes for implementing on said IC based on a score of said set ofdirect connection schemes.
 38. The method of claim 37, wherein each of aplurality of direct connection schemes of said first set of directconnection schemes has a symmetrical relationship with the other directconnection schemes of said plurality of direct connection schemes. 39.The method of claim 38, wherein two direct connection schemes have asymmetrical relationship when one of them can be generated by rotatingthe other through an angle.
 40. The method of claim 38, wherein twodirect connection schemes have a symmetrical relationship when one ofthem can be generated by reflecting the other about an axis.
 41. Themethod of claim 38, wherein two direct connection schemes have asymmetrical relationship when one of them can be generated by rotatingthe other through an angle then reflecting the other about an axis. 42.The method of claim 37, wherein generating said a first directconnection scheme of said first set of direct connection schemescomprises selecting a random set of direct connections.
 43. The methodof claim 42, wherein generating said first direct connection scheme ofsaid first set of direct connection schemes further comprises adding aset of direct connections that are symmetrical to said random set ofdirect connections.
 44. The method of claim 21, wherein a node comprisesconfigurable logic circuits and configurable interconnect circuits. 45.A method of generating a plurality of direct connection schemes forconnecting a plurality of configurable nodes in an integrated circuit(IC), said method comprising: a) generating a first direct connectionscheme comprising a set of direct connections from a given configurablenode to a set of at least two other configurable nodes; and b)generating a second direct connection scheme that is different from saidfirst direct connection scheme but is symmetrically related to saidfirst direct connection scheme.
 46. The method of claim 45, wherein saidsecond direct connection scheme comprises a rotation of said firstdirect connection scheme through a particular angle.
 47. The method ofclaim 46, wherein said second direct connection scheme further comprisesa reflection of said first direct connection scheme about a particularaxis.
 48. The method of claim 45, wherein said second direct connectionscheme comprises a reflection of said first direct connection schemeabout a particular axis.
 49. The method of claim 45, wherein said firstdirect connection scheme is asymmetrical and comprises at least twodirect connections.
 50. The method of claim 49, wherein said firstdirect connection scheme comprises at least four direct connections. 51.The method of claim 49, wherein said first direct connection schemecomprises at least six direct connections.
 52. A method of designinghardwired connections of an integrated circuit (IC) comprising aplurality of configurable nodes, said method comprising: a) specifyingan arrangement of configurable nodes; and b) performing a constrainedoptimization process to define an optimal set of direct connectionsbetween configurable nodes of said plurality of configurable nodes inview of a set of objectives.
 53. The method of claim 52, wherein saidoptimization process comprises: a) generating a plurality of directconnection schemes for connecting said plurality of configurable nodes;b) rejecting direct connection schemes of said plurality of directconnection schemes that do not fit a set of constraints; c) for each ofat least two direct connection schemes of said plurality of directconnection schemes, determining a quality of an IC using that directconnection scheme; and d) selecting a direct connection scheme thatoptimizes said quality and has not been rejected.
 54. The method ofclaim 52, wherein said constrained optimization process comprisessimulated annealing.
 55. The method of claim 52, wherein saidconstrained optimization process comprises local optimization.
 56. Themethod of claim 52, wherein said quality comprises a length ofconnections.
 57. The method of claim 52, wherein said quality comprisesa number of nodes that are reachable using no more than a particularnumber of direct connections in an IC using a given direct connectionscheme.
 58. The method of claim 52, wherein said quality comprises anumber of nodes that are reachable under multiple conditions in an ICusing a given direct connection scheme.